The element manganese which is considered essential for plants and animals is in high demand in industry as a whole. For example, manganese is used as a purifying and scavenging agent in the production of several metals such as iron, copper, chrome, nickel, aluminum alloys, alloy steels, etc., as well as being a source of manganese chemicals. Examples of manganese chemicals which find a wide variety of uses in the chemical industry include manganese acetate which is used in textile dyeing, as a catalyst in various chemical processes involving oxidation, in leather tanning and finishing, in paints and varnishes, etc., or manganese carbonate which is used in medicine, paint pigments, fertilizers, etc. These two manganese chemicals are only representative of the various types of manganese compounds which are used. One source of manganese metal is manganese dioxide, the natural form of which is pyrolusite. Another source of manganese which, up to the present time, has not been fully exploited is from sea nodules. Sea nodules are metal oxide masses which are found on the floor of various oceans and comprise mixtures of metals, the major components of these nodules being manganese and iron along with smaler amounts of nickel, copper, cobalt, zinc and cadmium. The processing of these sea nodules to recover the manganese as well as the iron, copper, nickel, cobalt, cadmium, etc., requires the presence of a reducing reagent in order to effectively recover the desired metal values. In the prior art these reducing agents have usually included sulfur dioxide, carbon monoxide, hydrogen, etc. As will hereinafter be shown in greater detail, it has now been discovered that manganese values may be recovered from manganese dioxide as well as from sea nodules along with other metal values which are present in said sea nodules in relatively high yields by subjecting the manganese bearing source to a roast in the presence of sulfuric acid and a reductant of a specific type which contains chromium.
This invention relates to a process for the recovery of manganese values from a manganese bearing source. More specifically, the invention is concerned with an improvement in a process for obtaining maximum manganese values from a manganese bearing source such as sea nodules in a series of steps hereinafter set forth in greater detail.
As was previously discussed, prior art methods for obtaining manganese from sources such as sea nodules required, in some instances, a reducing agent such as sulfur dioxide, carbon monoxide, hydrogen, etc., which were in gaseous form. The use of these gases as reducing agents required relatively complicated and expensive equipment including the use of pressure-resistant vessels in which to effect the recovery of the metal. In contradistinction to this, it has now been discovered that relatively high yields of manganese values may be obtained from manganese bearing sources by treating said manganese bearing source with an acid in the presence of a reductant which contains chromium followed by separation and extraction in a series of steps whereby a practically quantitative yield of the manganese in the manganese bearing source may be recovered.
It is therefore an object of this invention to provide a process for obtaining manganese from a manganese bearing source.
More specifically the invention is concerned with an improvement in a process for obtaining manganese from a manganese bearing source whereby the desired metal may be recovered in a substantially greater yield than has heretofore been possible.
In one aspect an embodiment of this invention resides in a process for the recovery of manganese values from a manganese bearing source which comprises subjecting said manganese bearing source to a roast in the presence of sulfuric acid and a reductant comprising a chromium-containing compound at an elevatated temperature, leaching the resulting pulp with water, filtering the leach solution to separate undissolved solids and pregnant leach liquor containing dissolved manganese ions and chromium ions, subjecting said pregnant leach liquor to solvent extraction with an organic solvent to selectively extract said chromium ion, separating the aqueous phase containing manganese ions from said organic phase, and recovering the manganese from said aqueous phase.
A specific embodiment of this invention is found in a process for the recovery of manganese values from a manganese bearing source which comprises subjecting sea nodules to a roast in the presence of sulfuric acid and chromite ore at a temperature in the range of from about 200.degree. to about 500.degree. C., leaching the resulting pulp with water, filtering the leached solution to recover a pregnant leach liquor containing dissolved manganese ions and chromium ions, subjecting the pregnant leach liquor to solvent extraction with an organic amine solvent to selectively extract the chromium ion, separating the aqueous phase containing manganese ions from the organic phase containing the chromium ions, subjecting said aqueous phase to an elevated temperature and pressure to precipitate manganese sulfate, filtering the resultant precipitate, leaching the precipitate to solubilize the manganese sulfate and separating said solubilized manganese from undissolved solids such as iron oxide.
Other objects and embodiments will be found in the following further detailed description of the present invention.
As hereinbefore set forth, the present invention is concerned with an improved process for the recovery of manganese values from a manganese bearing source such as manganese dioxide or sea nodules. In the process of this invention the manganese bearing source is combined with a reductant comprising a chromium-containing compound, a specific example of the chromium bearing compound being chromite ore. The use of chromite ore is desired due to its relatively greater availability and subsequent lower cost. The composition of the feedstock is accomplished by grinding the two components by means of a ball mill or any other method known in the art to a size preferably less than about 65 mesh (Tyler). The two components are then admixed after being ground to the desired size and thereafter pugged with concentrated sulfuric acid. By utilizing a feedstock comprising a mixture of sea nodules or manganese dioxide with a chromium-containing compound, it is possible to obtain a synergistic effect inasmuch as, as hereinbefore set forth, the manganese requires a reducing agent for optimum extraction, said reduction properties being afforded by the presence of the chromium-containing compound such as chromite ore. In the preferred embodiment of the invention the three components, namely, the manganese bearing source, the chromium-containing compound and the sulfuric acid are present in the mixture in a weight ratio ranging from about 1:1:1 to about 2:1:10 weight percent of manganese bearing source, chromium-containing compound and sulfuric acid respectively. In the preferred embodiment of the invention, concentrated sulfuric acid (about 90%) constitutes the acidic portion of the mixture, although it is also contemplated that sulfuric acid solutions containing less than the concentrated amount may also be utilized. While, as hereinbefore set forth, in the preferred embodiment of the invention, the manganese bearing source and the chromium-containing compound are present in a 1:1 weight ratio, it is also contemplated within the scope of this invention that the manganese bearing source will be present in a weight excess over that of the chromium-containing compound, said weight excess being in a range of from about 1.1:1 up to about 2:1 weight percent of manganese bearing source to chromium-containing compound. The pugged mixture of the three components is then placed in an appropriate vessel such as a pot furnace and subjected to a baking operation or roast which is effected in a range of from about 200.degree. to about 500.degree. C. and preferably at a temperature in the range of from about 350.degree. to about 400.degree. C. for a period of time sufficient to remove a major portion of the water content plus excessive sulfuric acid, the latter being fumed off during the reaction and, if so desired, recovered for admixture to form additional sulfuric acid. The aforesaid heating step is effected for a period of time ranging from about 5 minutes to about 30 minutes or more depending upon the temperature of the baking step and the amount of water and acid which is to be withdrawn. The aforesaid baking or roasting of the mixture will be effected until the mixture of manganese bearing source and chromium-containing compound is still in a damp state.
Upon completion of the baking or roasting step, the mixture is then leached with a sufficient amount of water and subjected to agitation for a period of time ranging from about 0.5 to about 4 hours or more while maintaining the temperature of the solution in a range of from about 25.degree. to about 95.degree. C. Following completion of the leaching step, the resulting solution is then subjected to a separation step such as filtration, decantation, etc., whereby the undissolved solids which comprise tailings are separated from the pregnant leach liquor, the latter containing dissolved manganese ions as well as dissolved chromium ions from the chromium-containing reductant compound. The pregnant leach liquor solution which may also contain other dissolved metal ions such as copper, nickel, cobalt, zinc, cadmium, etc., when the manganese bearing source comprises sea nodules is then treated for specific metal recovery of species other than manganese and iron or placed in an appropriate pressure-resistant apparatus. In this apparatus the pregnant leach liquor is subjected to superatmospheric pressures ranging from about 50 pounds per square inch to about 500 pounds per square inch as well as an elevated temperature in the range of from about 130.degree. to about 250.degree. C. The elevated temperature and pressure will precipitate the manganese as solid manganese sulfate. In addition, the iron which is also present will precipitate as ferric oxide. Upon completion of the desired precipitation time which may range from about 0.5 to about 4 hours or more in duration, the solid precipitates are separated from the liquids by any means known in the art such as filtration. The liquid portion of the solution will contain the dissolved chromium, copper, nickel, cobalt, cadmium, zinc, etc., metals if not earlier extracted or which may thereafter be recovered by solvent extraction. For example, the chromium may be selectively extracted by the use of tertiary amine compounds such as trimethyl amine, tributyl amine, tricapryl amine, etc., while the copper, nickel and cobalt which may be present are subjected to solvent extraction utilizing organic solvents of the hydroxy oxime type and thus may be selectively removed and recovered while the zinc and cadmium remain in the aqueous portion of the mixture. The aforementioned zinc and cadmium may then be recovered by any means known to those skilled in the art.
The solids resulting from the pressure precipitation of the pregnant leach liquor after separation from the aqueous liquid solution are then further leached, after being allowed to return to ambient temperature and pressure by treatment with an additional amount of water. After leaching the solution at ambient temperature and pressure for a period of time ranging from about 0.5 up to about 4 hours or more, the manganese sulfate which has returned to solution is separated from the ferric oxide which remains in solid form. This separation, as in the case of other separations hereinbefore set forth, is accomplished by filtration, decantation, etc., whereby the manganese sulfate is recovered in soluble form and treated by any means known in the art to recover the manganese in the form of metal or compound.